1. Field of the Invention
The present invention relates to a purine derivative having a cyclopropane ring, a process for preparing the same, and a process for preparing a cyclopropane ring-cleaved purine derivative from the purine derivative having a cyclopropane ring. The present invention also relates to a process for preparing a cyclopropane ring-cleaved compound.
2. Discussion of the Related Art
Conventionally, as to preparation process for purine derivatives useful for preparation intermediates for antiviral agents, there can be cited, for instance, a process disclosed in Japanese Patent Laid-Open No. Hei 3-120279. However, when the purine derivative is prepared from the preparation intermediates in the above preparation processes, its yield is as low as about 20 to about 40%. In addition, since extremely complicated procedures are necessitated in order to prepare the above preparation intermediates, there is a defect that the purine derivatives cannot be readily prepared as a consequence.
Therefore, recently, a development of a preparation intermediate which can be used in a process which can readily prepare a cyclopropane ring-cleaved purine derivative in a high yield and at high purity has been in demand.
In addition, there has been known to prepare a cyclopropane ring-cleaved compound by a process comprising hydrogenating a compound having a cyclopropane ring in the presence of a metal catalyst by the action of hydrogen gas as a hydrogen source; and cleaving the cyclopropane ring by reduction.
However, in this process, since it has been necessitated to pressurize the reaction system with hydrogen gas to a pressure of 3 to 5 kgf/cm.sup.2 upon hydrogenation, there arise such defects that the desired cyclopropane ring-cleaved compound has a low yield owing to the presence of large amounts of by-products in addition to the lack of operability and safety.
In view of the problems in the prior art, an object of the present invention is to provide a process for readily preparing a cyclopropane ring-cleaved purine derivative in a high yield and at high purity, a purine derivative having a cyclopropane ring which can be suitably used in the above process, and a process for preparing the purine derivative having a cyclopropane ring.
Another object of the present invention is to provide a process for preparing a cyclopropane ring-cleaved compound with excellent operability and safety in a high yield.
These and other objects of the present invention will be apparent from the following description.